At many industrial and commercial facilities throughout the United States, soil and groundwater have become contaminated with organic pollutants. Accidental spills have occurred at other sites contaminating both soil and groundwater. A variety of techniques have been developed for the removal of these contaminants. One common technique is soil excavation and off-site treatment of the soil, which is often very expensive. Another treatment involves air sparging technology using the controlled injection of air to strip organic compounds from the water or to supply oxygen for bioremediation of the contaminants. However, complex aromatics and other large molecules are often resistant to sparging and bioremediation, thereby requiring more complex and expensive treatments. Many recalcitrant organic compounds, such as carcinogenic polychlorobiphenyls (PCBs), phthalates and organopesticides have proven particularly difficult to clean up.
Ozone is a gas with strong oxidizing properties. It is commonly generated by forcing oxygen through narrowly spaced electrodes under a high voltage known as the corona discharge method. The first commercial uses of ozone occurred in Europe in the late 1890""s for the treatment of drinking water. Since then, ozone has been widely used for the treatment of drinking water and wastewater.
In the October 1997 issue of Soil and Groundwater Cleanup, an article (xe2x80x9cBubbles Spell Trouble for Chlorinated Solventsxe2x80x9d) by William B. Kerfoot discloses the injection of air/ozone into groundwater to reduce the levels of volatile organic compounds (VOCs) such as PCE (polychloroethylene), TCE (trichloroethylene) and 1,1 DCE (dichloroethylene) contained therein.
U.S. Pat. No. 5,269,943 issued to Wickramanayake discloses that ozone can be successfully used to treat unsaturated soil contaminated with organic pollutants only if the ozone is first pretreated with an acid. Wickramanayake teaches that simply applying unacidified ozone to unsaturated, contaminated soil apparently forms ozone scavengers causing the ozone to decompose too rapidly and making such ozone treatment unfeasible.
It is an object of this invention to provide a method of reducing the concentration of recalcitrant organic contamination in a soil matrix using unacidified ozone.
It is a further object of this invention to provide a method of substantially reducing the concentration of recalcitrant organic contamination in a soil matrix in a rapid manner.
It is still another object of this invention to provide a method of reducing the concentration of PCBs and other extremely recalcitrant organic contaminants in a soil matrix.
The present invention provides a method of reducing the concentration of recalcitrant organic contamination in a soil matrix. The method includes the steps of incubating the contaminated soil matrix with unacidified ozone sufficient to reduce the concentration of the recalcitrant organic contamination in the soil matrix by about 10% to about 15%; and then applying unacidified ozone to the soil matrix sufficient to substantially reduce the concentration of the recalcitrant organic contamination in the soil matrix. During the incubation phase, the ozone demand of competitive, non-contaminant ozone consumers in the soil is satisfied. Additionally, during the incubation phase, ozone conditions the contaminated soil matrix to prepare the recalcitrant organic contamination for subsequent rapid and substantial destruction. When the concentration of the recalcitrant organic contamination has been reduced by from about 10% to about 15% in the soil, the incubation phase has ended such that the application of additional unacidified ozone to the soil matrix rapidly and substantially reduces the concentration of the recalcitrant organic contamination in the soil matrix.